Notions of upward compatibility of temporal query languages

Migrating applications from conventional to temporal database management technology has received scant mention in the research literature. This paper formally defines three increasingly restrictive notions of upward compatibility which capture properties of a temporal SQL with respect to conventional SQL that, when satisfied, provide for a smooth migration of legacy applications to a temporal system. The notions of upward compatibility dictate the seman- tics of conventional SQL statements and constrain the semantics of extensions to these statements. The paper evaluates the seven extant temporal extensions to SQL, all of which are shown to complicate migration through design decisions that violate one or more of these notions. We then outline how SQL-92 can be systematically extended to become a temporal query language that satisfies all three notions.